Gentlemen, I've been fighting a fueling, open loop issue after three hard pulls at WOT last week. I'm not sure if it was after the first or third pull when I notice my AFR at idle to be 17.6 and not the normal 14.5 indicated previously. The car running very rich with unburned fuel observed on top of the pistons and exhaust temps measured at the exhaust manifold runners to be around 225 degrees. My mind immediately went to a vacuum hose that had became disconnected, blown off under 10lbs of boost. I also later discovered my car's SC ECU was in "open loop" and my O2 sensors all reading 5 volts but for one O2 sensor (B) . Since I've only one 3" down pipe with a single high-performance cat; I've mounted two O2 sensors before the cat and two O2 sensors after the cat; it's easy to tell if an O2 sensor not responding like its adjacent roommate. I replaced the O2 sensor and according to the IDS software, all four O2 sensors at 5 volts but will only switch high to low when I modulate the throttle. Attempts to perform an O2 orientation procedure failed half way through the procedure. I believe it failed to finish the test because my O2 sensors are essentially in the same "bank" and the ECU could not differentiate between A and B or C and D. Finding no visual evidence or not hearing a vacuum leak, I connected my smoke machine and discovered a little bit of smoke escaping from a few hose clamps. Tightened all clamps and restarted car and my AFR now at 16.5, better but not where it was. I intentionally pulled a vacuum hose and AFR went to 20.2, exactly what I would expect. Replaced fuel pressure regulator with a Bosch unit I'd purchased new several years ago suspecting I'd damaged it under boost with no effect. ECT read 168 degrees, pulled plug and scanner read -40 degrees, shorted ECT and scanner read 308 degrees with no effect on high AFR reading. The AFR only high at idle and immediately falls to 14 and below with the smallest amount of throttle manipulation; my brain telling me it's a classic vacuum leak overcome by more air entering the throttle body when opened. So after smoke testing and other machinations, I exposed my AEM air filter element so I could access and placed a plastic FedEx bag over it. In theory this should stall the car or cause my AFR to go very rich (no air). After placing the bag on the filter element the bag immediately vacuum formed to the filter element and the MAF reading fell from 1.3 volts to .75 volts; in addition, all my silicone elbows began to collapse flat under vacuum from the filter element being sealed off. You guessed it, my AFR still reading 16.5, unchanged! Had I a vacuum leak sufficient to keep the engine running with an unchanged AFR reading I would have heard it, the smoke testing aside.

Now my mind racing ahead 7 months to my every two year rendezvous with the state's emission testing facility, I thought I had this nut cracked! In an attempt to further troubleshoot the issue I swapped in my normally aspirated ECU, leaving the 30lbs injectors in place. To my surprise, the car went in to closed loop mode, the O2 sensors switching high to low but AFR at 9.10 I then swapped out the 30lb injectors with 19lb injectors and reinstalled the NA MAF and AFR returned to 14.5 and the ECU in closed loop with the O2 sensors behaving normally. A test drive saw 2 of the 5 INC readiness monitors reset and I'm confident with a few more drive cycles all would have eventually reset and I'd have no issues passing my state's emission requirements in this configuration. This configuration also ruled out a serious vacuum leak or other sensor failure causing the high AFR. The downside, my car's performance just stock, the NA ECU doing a fine job to keep the AFR at around 14 but the turbo would barely spool; I'll call this configuration my emission testing configuration but very unsafe, to lean for extended turbo operation. FYI- my exhaust runner temps increased to 300 degrees on average in this configuration; evidence the car probably more efficiently burning fuel and air.

So now I'm back to the SC ECU, what happened under those WOT pulls to have it start producing a very high AFR at idle and over fuel the engine? @XJRengineer Is there a table that could have been corrupted making WOT pulls with a NA MAF sensor? I made the pulls prior to @Larry Louton sending me an SC MAF to test with. I've purchased another SC ECU and hoping to have it this week to do a side by side comparison to see if the combination of the SC MAF and SC ECU will return idle AFR to normal and prevent the fueling issues I'm experiencing now. To be clear, the fueling issue is only at idle; off idle, the AFR readings between are between 14 and 11.75 and the turbo loves it!

Looping in all forum members to make sure I'm not overlooking the obvious.

Thanks,

 

Hello Sparkman, You haven't mentioned anything about your Throttle position sensor or leaking injectors. Does your laptop do individual injector pulse? Have you done a hard reset? How is your manifold vacuum?
That is what comes to my mind looking at your notes.

Larry Louton

 

I was going to suggest disconnecting MAF to make sure it is not the case as I had massive over fueling with bad MAF, and by massive I mean diesel like black smoke over fueling. But looks like you are getting logical MAF signal rereading the original post. Anyways would be easy and fast check; just disconnect the MAF plug and see what the air-fuels do?

rereading :
"MAF reading fell from 1.3 volts to .75 volts" if this was at idle and with the SC MAF, it does seem to be on the high side?

 

unplug the MAF and see how the failsafe map runs, stfts are normally like -25 at idle. if you have a later car you have to remove it while running but earlier cars will start and run without it.

 

@Larry Louton Larry thanks for the response, even though my TPS output looks normal (0-5V) I went ahead and used the IDS to perform a throttle position sensor adaptation without issue. I would think all injectors would have to be leaking for all pistons to have unburnt fuel on top of them. Manifold vacuum at -16 to -18 psi at idle. If a "hard reset" involves cross connecting negative and positive leads for an extended period of time (overnight) then yes.
@AnttiM Disconnecting the MAF drives the AFR from 16.5 to 10. The MAF voltage at idle does appear to be high and the reason I tried to restrict airflow through the AEM filter and turbo inlet. Interestingly, when I barely crack the throttle plate AFR falls to 14.5. I'm wondering what effect manipulating the adjustment screw for the throttle stop would have. Would opening the throttle plate just a tiny bit positively effect AFR and would IAC valve work to control idle? Despite manipulating the throttle to achieve perfect AFR ECU will not go into Closed Loop mode.
@xalty MAF disconnected, AFR drops to 10. No short fuel trims indicated in Open Loop mode. I do have some PID in my scanner's stream way down the list (different from the STFT PID) that indicates fuel trims to be 99%

Interestingly, when I exchanged the SC ECU for the NA ECU, leaving in the 30lb injectors the AFR was 9.1 (supper rich) Despite being super rich the NA ECU was in the Closed Loop mode and I had both LTFT and STFT readings. Trying to figure out why my SC ECU went into Open Loop. Are my readings high because I'm in Open Loop or am I in Open Loop because my reading are high; chicken or the egg scenario. My new SC ECU shipping out of Pennsylvania this week and hopefully the answer/solution will become more obvious when I'm able to test with another SC ECU.

Don't get me wrong, this problem is very manageable. Either run it this way until it's time for my emission test and then revert the configuration back to stock with 19lb injectors, NA MAF and NA ECU. I could also reinstall the Haltech ECU along with the NA ECU and have the Haltech just control just the fueling by entering "target" AFRs for each of the break points for load and rpm. If the new SC ECU reacts just like the SC ECU I have, I may go back with the NA ECU and Haltech to control fueling. If the new SC ECU comes up in Closed Loop mode and appears to accurately control the fueling, I may attempt to copy the ePROM files from the working SC ECU and write the files to my original SC ECU running in Open Loop mode. I've got an ePROM reader/burner somewhere, but would have to dig up an old machine having a a parallel port.

Thanks and keep the ideas coming. The best way to fix a problem is to rule out everything else.

 

Tangential thought: The afr ratios you mention are based on data from your O2 sensors. Air getting into your exhaust at a manifold or downpipe flange would weaken your apparent mixture without weakening your actual mixture. The amount would be tiny, hence having a proportionally smaller effect as soon as you begin to open the throttle. Doesn't explain why it goes away with different injectors etc, but your WOT runs could have blown a small leak?

 

Coming back to the original post :" Gentlemen, I've been fighting a fueling, open loop issue after three hard pulls at WOT last week. I'm not sure if it was after the first or third pull when I notice my AFR at idle to be 17.6 and not the normal 14.5 indicated previously. " The configuration at this point was SC MAF + SC ECU ? And did the car work normally (normal AFR, normal voltage reading at MAF) at any point with the SC MAF? I am just wondering did the SC MAF start malfunction on the WOT pulls as my MAF died on WOT pull ...

 

@countryjag and @AnttiM I think you may have uncovered a clue I had not considered. The AFR is measured with an AFR gauge and sensor mounted near the exit of the turbo's downpipe. Yes, my SC ECU was in Closed Loop before the wide open throttle pulls but maybe the stress from the wide open pull cracked or caused an air leak in my waste gate or exhaust circuit near the AFR sensor? That may explain the high AFR readings at idle and AFR readings that return to normal when the throttle cracked open. It now sounds like I need to connect my smoke machine to the exhaust side to check for leaks near and around the aftermarket AFR sensor. Thinking out loud here, still, that would not explain why when the NA ECU swapped for the SC ECU, the AFR, as measured by the same sensor returns to normal and my NA ECU is in Closed Loop mode. If cracked and leaking air, you'd think the AFR would read high regardless of the ECU used. Maybe the SC ECU "base fueling" table just to lean at idle? Since I'm in Open Loop mode I'm just using a base fueling table, but if that's the case why does my AFR go rich when I disconnect the MAF sensor? That would indicate I'm not just using a base fuel map alone. I just pinged the wrecking yard in Pennsylvania requesting ETA on the used SC ECU I just purchased; swapping it in may shed additional light on this mystery.

Thanks for everyone's response,

 

Three things come to mind with this problem. One would be a ruptured canister purge valve. Second would be a crankcase ventilation problem or leaking gasket/seal I.E. cam cover gaskets/seals, crankshaft seals etc. Third would be a brake booster problem. These are just off the top of my head from past experience on various vehicles.

 

@Darren_M Thanks for the feed back and all good suggestions. A clue that may have been over looked in my original post is that when I normalized my configuration, by reinstalling the 19lb injectors, reinstalling my NA MAF and NA ECU; the AFR, fuel trim readings return to normal and the NA ECU is operating in closed loop mode. In my mind, that rules out any other other system or malfunction that could affect AFR and fuel trims with the SC ECU installed. Sadly, the salvage yard I'd ordered another SC ECU from on October 15th has been unresponsive in my attempts to learn the ECU's shipping status and ETA. I was hoping to have it by now to compare and possibly confirm something has happened to my original SC ECU. Again, because my STFT's close to 0 (-1.2) when the NA ECU and 19lb injectors are reinstalled, I'm suspecting something has happen to my SC ECU.

Your stable of cars, trucks and motorcycles is very impressive and the reason I choose to live inside the St. Louis city limits. If I lived outside the city and had some acreage, my wife's greatest fears would come true, I too would own one of everything.

Take care,

 

Without me taking the time to see what the ECU controls and under what circumstances it does operate them I have seen those 3 items be a problem that comes and goes depending on the ECU operation. I know that seems odd but I have seen brake boosters fail once a certain vacuum level is reached, along with canister purge valves and PCV systems. At any rate, with all you have designed doing this I am impressed. Maybe collecting some hard data out side of the normal acquired data from the ECU is in order. I would be curious of what the data map overlays are between the 2 of them. Also I would love to see some scope data from the injectors to see when the pintle is opening and closing and also to see if the injector drivers are working properly. COuld be that after a few hard pulls like you did may have pushed something over the edge? Also, since it appears only at idle, throttle closed - it is possible you may have some injector spray pattern problems causing the fuel to be slightly restricted or not producing a proper spray cone. Just thoughts to consider, this is how my mind works when chasing little buggers like this.

As for my "fleet", that is just a portion of them along with other bad habits like collecting antique garden tractors and restoring/rebuilding machine shop equipment along with my daily job of being an auto repair shop owner and tech just to name a few.

 

And it just dawned on me that this weekend has me passing through St. Louis today and again Sunday....

 

Hello Sparkman, I have two used, possibly ruined 1995 XJR AJ16 ECM's if you want them for free. Send address again.

Larry Louton

 

Ok lets stop playing mix and match for a second because its not good for the engine to put in a component that isnt meant for it. Plus im not sure you are reading the results right because we dont know how na components in an sc motor are going to influence the ecm so any results are not going to tell us much of anything.

The engine is a system. all the individual components of that system are sized appropriately and matched together so the ECM can adequately control the inputs to the system to make it run right. Start feeding the ECM wrong information and the ECM is going to do the wrong thing.

it sounds to me like your engine is going into open loop mode. at idle, high AFRs (lean) won’t really hurt it. So maybe that 17 AFR which is super lean is just a failsafe mechanism of the ECm. I know that in my hellcat my ECM gives me extremely lean AFR‘s when I’m decelerating or coasting and that’s normal. I’m not sure but it sounds reasonable that its going to some restricted mode or open loop mode at idle and that’s why as soon as you give it throttle it goes back to a map and riches it up.

this all happened after a couple of wide-open throttle runs. Vacuum goes to zero at wide-open throttle so it’s not as if at wide-open throttle you blew open your brake booster or your PCV valve. Maybe on deceleration you created a high vacuum but even in that situation I can’t see it blowing out one of those components because they are sized to be able to handle deceleration as it happens every time you drive.

however wide-open throttle does create a lot of stress on components and it causes a lot of pressure in the intake track and in the exhaust track. So I would be looking at something which could have been blown out or split or collapsed due to pressure such as catalytic converter‘s or timing belt slipping or spark spark plug melting.

stop swapping in normally aspirated components as that is not going to help us at all and might just mess us up more put everything back the way it supposed to be. Pull the plugs and look at the colors. Make sure you didn’t melt the electrodes. Pull the cats off and make sure they’re not collapsed or melted. Check the wastegate. Look for things down stream of the blower where theres high pressure. Look at things that might be damaged by force. as well as things in the motor which might have to let go such as the top of the piston or a ring creating excessive pcv flow causing extremely lean mixtures. Definitely do a smoke test. Maybe do a compression test. Let’s get some data such as what is your timing are all of your injectors firing equal amounts or is one stuck. Start from the beginning and less work at through

 

@Aarcuda Agree with your conclusions up to a point; I've turbo charged a normally aspirated engine and trying to figure out what combination components work best. For months, I ran my stock NA ECM, NA MAF, and supercharged 30lb fuel injectors with a Haltech Elite 750 wired in piggyback mode to control fuel and timing. I then scored an ECM from a supercharged version of my car and replaced the original NA ECM and piggyback Haltech ECM with the SC ECM. This combo made a lot of power at WOT but I was over fueling with the NA MAF under normal driving conditions. Thanks to all on this forum and @XJRengineer , I discovered the supercharged version of this engine uses a different MAF programmed with a different MAF curve. @Larry Louton Kind enough to send me the supercharged version to test with (Larry let's chat about the MAF sensor you sent, I'll send my cell number in PM). After installing a MAF for a supercharged engine the fuel trims were not as rich as when using the NA MAF but it was too lean prior to turbo spool; it would eventually go rich enough (12.5) at wide open throttle but not before going super lean on throttle tip in. I went back to my NA MAF but blocked off two of the four sensor ports in the MAF housing in an attempt to "slow" the air passing by the sensor. Blocking off two of the ports caused the AFR to go from way to rich to way to lean. I then drilled a 1/8" hole in one of the blocked MAF sensor ports. Fuel trims were perfect at cruising speeds, pre-boost, but way to lean under boost. I then drilled another 1/8" hole in the other blocked sensor port and now fuel trims where I need them to be, 14.5 cruise/pre-boost and dropping to 11.5 at wide open throttle. The modified NA MAF super responsive compared to the SC MAF and I am not suffering the lean condition on throttle tip in. I'm not blaming the SC MAF but maybe turbo spool time and supercharger response times very different; the modified NA MAF response and fuel trims just seems to work better than the stock SC MAF.

Until I score another SC ECM to test with, this is the configuration I'm going to run; no check engine light or codes pending but in "open loop". Lots of power at 12psi of boost (yes, I increased it another 2psi) but I think I've finally found the limits of my injectors or fuel pump; maybe both. Come July 2021, I've got to reinstall the original ECM, injectors, stock MAF, clear any codes and reset all monitors to pass state emissions.

Thanks to all for the advice and support,

 

Still looking for a appropriate box to ship the Two ECM's in plus a AFM from a NA vehicle that you can carve up any way you want. I remember seeing slots in the interior housing but how you filled the slot's then drilled holes would
be very enlightening to see. Perhaps using multiple small holes or slots that size wise equal the area of the hole that you've all ready drilled could used for tuning purposes. What happened to the two ECM's that the Short term values would operate normal but the Long term kept going to the minus and going and going and going and would not return despite my efforts. The other one I think is a N/A ECM with a S/C cover on it that I believe I got cheated on.
Larry Louton

 

your trails and
tribulations of all of the different attempts you made which ended up with other predictable erroneous responses only support my statements above. I was an EE. I used to be the guy who would troubleshoot high end electronic assemblies on critical programs so i had strict rules on how i can troubleshoot it to root cause. I wasn’t allowed to touch any of the failed units until I could describe all of the potential faults that would produce the anomalous observables. After identifying of the potential causes, I then had to produce a plan to troubleshoot step-by-step with various branches to take depending on the results i got so that we do not lose the fault and we do not cause more damage. The idea of swapping things in Without knowing what the results should be and knowing that the results will be safe would never occur in our business.

lol I guess they’ve conditioned me so well that I’m afraid to take chances on On these networked systems without knowing what happens inside each of those black boxes in our vehicles. But I know that because of the way a supercharger produces boost that the throttle Tip in and fuel tables are managed completely differently In a supercharged vehicle than a normally aspirated vehicle. Unless you happen to run across the right combinations of Band-Aids and fixes that produce other problems without blowing the vehicle up in the meantime - it’s risky.

anyways. A logical approach using know good parts design for the system is always the best route unless its sll you got I guess